There are many known methods to authenticate a document such as a scratch off lottery ticket, on-line lottery ticket, receipt, bet-slip, admission ticket, delivery slip, etc. to help prove that the document is authentic. For example, the most basic methods include imposing or embossing a visible seal on the document, using a watermark, using a color shifting ink, etc., all of which are readily visible to a person viewing the document. Other methods include the use of microprinting or heat or light sensitive ink.
One technique for document authentication includes encoding authentication information and other data into optical identifiers or other markings printed or embedded on the document. In addition to document authentication, optical identifiers may be used to provide copyright protection or to encode additional information such as information relevant to a particular lottery game in the case of a printed lottery ticket.
Optical identifiers may include, for example, printed one-dimensional or two-dimensional barcodes or embedded optical patterns that define optical signatures for the document. Exemplary optical signatures for use in authenticating lottery tickets are disclosed in U.S. Pat. Nos. 7,252,222 and 7,364,091 which are incorporated herein by reference for all purposes. Optical signatures may be defined by variety of optical patterns that may be printed or embedded using a variety of types of ink or printing techniques. For example, certain optical patterns may be printed using infrared responsive ink that is invisible under white light.
To process an optical identifier or other marking, a document reader including a scanner or camera is used to capture a digital image of the document. An inexpensive camera, linear sensor, or contact image sensor may be used to provide this image capture functionally. Once the document reader has captured a digital image of the document, various processes and analyses are performed on the document image to determine, for example, if the document is authentic. These processes may include decoding authentication information or other data encoded into an optical signature or barcode. An exemplary document reader is disclosed in U.S. patent application Ser. No. 12/200,367 which is incorporated by reference for all purposes.
Proper analysis of optical identifiers and other markings using a camera-based document reader requires a substantially flat and undistorted image of the optical identifier or other marking. This presents a challenge as images captured by the reader may become distorted due to folds and wrinkles in the document placed in the document reader. Thus, document readers must be able to provide a corrected document image that removes imperfections caused by folds or wrinkles in the document scanned by the reader.
In the general case of image deformation on a slope, the image may be corrected using known trapezoidal correction techniques or other known techniques. However, to apply these techniques correctly, geometric information about the document such as the initial shape and size of the document must be known. This presents a further challenge due to documents varying widely in shape, size, and color. For instance, instant scratch off lottery tickets are available in a wide variety of shapes, sizes and colors.
Document size and shape may be determined using optical identifiers or other markings printed or embedded on the document, such as the game number in the case of lottery tickets. For example, the optical identifiers or other information embedded on the document may be linked or associated with geometric or other document information stored in a database. However, decoding the optical identifiers or other markings when the correct shape and image resolution of the document are unknown is a problem in its own right. Indeed, the optical identifiers may be so distorted that they cannot be properly read or scanned by the document reader.
The use of optical identifiers with more robust orientation marks in conjunction with a quiet zone may be capable of being decoded despite the presence of folds and wrinkles in the document image. For example, certain one-dimensional or two-dimensional bar codes may be capable of being decoded by a document reader despite imperfections in the document image caused by folds and wrinkles in the document placed in the reader. However, these robust optical identifiers usually take up significant document space and may be undesirable for use in many documents. For instance, such robust identifiers may not be desirable for use on instant lottery tickets because of their impact on space available for instant ticket graphics and play area.
Thus, a need exists for enabling image correction of documents in an optical reader that overcomes these deficiencies. The present disclosure provides a document having an optical pattern that is decoded by the optical reader to determine an optical signature associated with geometric or other information about the document. The optical pattern may be a part of the background pattern of the document or otherwise camouflaged to the holder of the document. The document reader uses document classification information associated with the optical signature to apply image correction techniques and to provide a corrected document image.